This invention relates generally to the field of motion monitors for patients, and more particularly to an improved monitor for bio-mechanically characterizing falls in patients and providing an alarm in case of a fall.
Our aging population, improved health care, and an increasing number of working women create a demand for technologies allowing older persons to live independent lives. This number, in the U.S. alone, is estimated at 27 million people and will grow to 50 million by the year 2010. Thus, there are significant needs in the development of assistive technologies that allow older people to live alone safely.
Health-threatening falls are an important epidemiological problem in a growing segment of the aging population. Studies indicate that approximately two thirds of accidents in people 65 years of age or older, and a large percentage of deaths from injuries are due to falls. It has been estimated that approximately 1.6 million hip fracture injuries worldwide in 1990 were due to falls, and that this number will increase 6.26% by 2050, with the highest incidences recorded in Northern Europe and North America. In the elderly, 90% of hip fractures happen at age 70 and older, and 90% are due to falls. The falls are usually due (80%) to pathological balance and gait disorders and not to overwhelming external force (i.e., being pushed over by some force). More than 50% of elderly persons suffer from arthritis and/or orthopedic impairments, which frequently leads to falls. Specifically prone to falls are women experiencing a higher percentage of arthritis-related structural bone changes. It is estimated that approximately 5% of falls result in fracture and 1% of all falls are hip fractures. The percentages vary slightly in different geographical regions (e.g., Japan, Scandinavia), but the consensus of the available research is that the falls are a significant epidemiological problem in the growing elderly population.
Among older people in the U.S. (age 65+) there are approximately 750,000 falls per year requiring hospitalization due to either bone fracturing (approx. 480,000 cases) or hip fracturing (approx. 270,000 cases). The result of such injuries is an average hospital stay between 2 and 8 days. Assuming the average cost of $1,000 per hospital day, a total cost of falls in the elderly for the health care industry can be estimated at three billion dollars per year. This figure is likely to increase as the older aged segment of the population increases.
Falls in elderly people have been recognized as a major health problem in an aging population. Physical activity patterns, detecting the occurrence of falls, and recognizing body motion patterns inevitably leading to falls are not well understood due to the lack of systems which allow continuous monitoring of patients in an accurate, convenient, unobtrusive and socially acceptable manner.
This invention provides a method for monitoring a person""s fall using an accelerometer included in a personal monitoring device configured to be carried on the person. The monitoring device has a microprocessor and a memory buffer, and data is stored in the buffer of the personal monitoring device. The first step in the method is sampling an output from the accelerometer indicative of body acceleration and body angle. The next step is detecting whether the body angle is in a steady state indicative of a fall for at least two seconds. Then the fall duration is measured by reading back through the buffer. Another step is determining if an uncontrolled fall has taken place by testing whether the fall duration is less than a time threshold. The last step is determining whether a severe fall has occurred by comparing an angular rate of change of the body angle and an acceleration amplitude change to a severity threshold.
In accordance with another aspect of the present invention, the method monitors a person""s fall using a single-dimensional accelerometer in a monitoring device on the person. The method includes the step of detecting whether the person""s acceleration exceeds a maximum threshold. The next step is collecting at least 2 seconds of additional acceleration data in a buffer. Another step is finding a largest acceleration sample value in the buffer. The final step is signaling that a fall has taken place when that acceleration sample value exceeds a predetermined maximum threshold.
Additional features and advantages of the invention will be set forth in the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate by way of example, the features of the invention.